RFR: 8326306: RISC-V: Re-structure MASM calls and jumps [v6]

[Robbin Ehn]

> Hi, please consider.
> 
> We have code that directly use the asm for call/jumps instead masm.
> Our masm have a bit odd naming, and we don't use 'proper' pseudoinstructions/mnemonics.
> Suggested by [riscv-asm-manual](https://github.com/riscv-non-isa/riscv-asm-manual/tree/master)
> 
> j offset	jal x0, offset	Jump
> jal offset	jal x1, offset	Jump and link
> jr rs	        jalr x0, rs, 0	Jump register
> jalr rs	        jalr x1, rs, 0	Jump and link register
> ret	        jalr x0, x1, 0	Return from subroutine
> call offset	auipc x1, offset[31:12]; jalr x1, x1, offset[11:0]	Call far-away subroutine	
> tail offset	auipc x6, offset[31:12]; jalr x0, x6, offset[11:0]	Tail call far-away subroutine
> 
> But these can only be implemented like this if you have small enough application.
> The fallback of these is to use GOT (your C compiler should place a copy of GOT every 2G so it's always reachable).
> We don't have GOT, instead we materialize, so there is still differences between these and ours.
> 
> This patch:
> - Tries to follow these suggested mappings as good we can.
> - Make sure all jumps/calls go through MASM. (so we get control and can easily change for sites using a certain calling convention)
> - To avoid confusion between MASM public/private methods and ASM methods and the mnemonics there are some renaming.
>   E.g. the mnemonics jal means call offset, as we can't use that so there is no 'jal'.
> - I enabled c.j, but right now we never generate it.
> - As always the macro does no good and are legacy from when code base did not use templates. (also the x-macros screws up my IDE (vim+rtags))
> 
> I started down this path due to I have followup patch on top of this which removes trampoline in favor for load-n-jump.
> (WIP: https://github.com/robehn/jdk/compare/jal-fixes...robehn:jdk:load-n-link?expand=1)
> While looking into our calls it was a bit confusing, this helps. 
> 
> Done a couple of t1-3 slightly different version of this patch, and as part of the followup, no issues found. (VF2, qemu, LP4)
> Re-running tests, had some last minute changes.
> 
> Thanks, Robbin

Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:

  Use li instead of movptr

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/18942/files
  - new: https://git.openjdk.org/jdk/pull/18942/files/6b3e4c47..d8fbb00b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18942&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18942&range=04-05

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18942.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18942/head:pull/18942

PR: https://git.openjdk.org/jdk/pull/18942